anyone tried or even seen them despite their high costs ?looks like the way to go ,they last 20 years without a re charge ¬i dont know how common or what price is tritium to make the batteries .sound s like a job for Doc Oc

The half life of tritium is 12.32 years. It's not going to last 1000 years. After 100 years only 0.36% will remain. After 1000 years, 3.7E-25. I'm sure the betavoltaics have a cutoff threshold at some point where there is no voltage despite some residual beta activity.